A protester unfurled a banner stating 'NRA Killing Our Kids' during a National Rifle Association press conference being held after the Sandy Hook school shootings.
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The Duchess of Cambridge has been on maternity leave since the week before Easter.
The Duke and Duchess of Cambrige have been together for 15 years and will have three children under the age of four.
News of William and Kate’s third child was announced on September 4 and the duchess went on maternity leave on March 22.